Impregnating wood



Patented-Feb. 1c, 1926..'

T ED. A. E s

PAT

OTHiO V. STEWART, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC 8c MANUFACTURING: COMPANY, A CORPORATION 01E PENNSYJU" VANIA.

No Drawing.

, Impregnating Wood, of which the following is a specification.

This invention relates to the impregnating of wood, more especially to the mpregnating of wood strain-insulators for use in highvoltage transmission lines.

Such insulators should have relatively great strength, be impervious to moisture, and have excellent insulating properties. The present invention is designed to produce an insulator of the above type, which is very resistant to moisture and to changes in atmospheric conditions, which has great mechanical strength and is an excellentinsulator. 4

In order to produce a strain-insulator of 'wood having such desirable properties, it

has been attempted, at various times, to treat wood sticks by various methods, such as seasoning the wood, boiling or steaming the same, impregnating with various substances, such as gums, oils,.or waxes'ofvarious kinds under pressure, or-at atmospheric pressure, or in a partial or complete vacuum. A favorite niethodof impregnating has consisted in placing sticks under a vacuum and subjecting the same to heat for a considerable length of time. During this vacuum-and-heat treatment,asphalt was allowed to come in contact with the wood at the elevated temperature in orderfto impregnate the same. A further treatment, consisting in applying pressure to the heated'masszso treated, was then usually employed.

Such processes had many disadvantages in that the gummy orasphaltic material penerated but slightly below the surface of the wood, rarely ever penetrating more than one-eighth of an inch in depth; Furthermore, these processes were complicated and relatively expensive, since they usually utilized a vacuum or pressure, or both. For this reason, it was generally necessary to treat the material in closed vessels. On account of the viscosity of the asphalt or other similar material used, the impregnation was not uniform and the impregnated wood was, therefore, not uniformly resistant to the temrials will IMPREGNATING 'woo Application filedDccember 16, 1320. Serial No. 431,289;

perature and moisture changes in the atmosphere. The interior of the wood was generally not impregnated at all, and, since the impregnation of the surface was not uniform, moisture often entered the interior and caused deterioration of the wood. a

. In practising myiinventio n, I impregnate the wood, preferably partially dried, with a substance which penetrates easily and is capable of filling all the pores of the wood. This material may be a relatively light substance which melts at a low temperature and has' a relatively low boiling point. It is merely necessary that this substance be an insulator and have a low viscosity in order to more readily penetrate the wood. I I subsequently treat the wood so impregnated with a heavy non-volatile material which coats the outer portion of the wood, preventing the loss of the first substance which penetrates the entire body-of the wood and thus increases the thereof and insures the exclusion of moisture insulating properties therefrom. The substance, which I prefer to use for the first impregnation, is a wax, such as parafiin, and for the second treatment, I prefer to use a such as an asphalt.

My new process is preferably carried out as follows: Wood is cut to the proper size and shape and is then kiln-dried until the moisture content is about ten to twelve per cent. The wood is then immersed in a bath of molten paraflin, which is at a temperature generally not exceeding 130 0., for a period of from five to'six hours. The wood is removed from the paraffin bathand immersed in a bath of molten asphaltic material, which is heated to a temperature ofabout 150 C for a period of from three to four hours.

The action which takes place under this procedure is believed tb be as follows: It is well. known that paraffin or similar matepenetrate the pores of wood rather readily, whereas a heavier material, such as asphalt, will penetrate very slightly, due to the higher viscosity thereof. By. first im-' pregnating the wood with paraffin andthen gummy material,

which is drawn into-the individual cells of the wood by reason of the partial vacuum created therein. By this treatment, I am ,tration of asphaltic material than hitherto,"

enabled to vproduce a much greater penemany tests showing a penetration of from three-eighths to one-half'inch', whereas, by

former methods, the asphaltic material did not generally penetrate more than one-eighth inch. I r

This process of impregnating wood gives a high dielectric strength thereto without any loss of mechanical strength and simultaneously renders the wood moisture and weather-proof. The heat of thesun has practically no effect upon the impregnating materials which are not evaporated under 'still remain open. If the moisture content should be reduced to a substantial degree great resistance to electrical strains. For

below ten per cent, most, or many, of the pores would become closed and would offer relatively great-resistance to the penetration of the paraffin. I v

The central portion of the insulator. being filled with paraffin, is rendered moisture-v proof so that, even if the outer layer of asphalt is defective, moisture will still be unable to enter the wood and impair the insulating properties thereof. The asphaltic material along the outer portion also aids in rendering the 'woodmoisture-proof and water-resistant and, being non-volatile, remains permanently in place, preventing the relatively volatile paraflin from escaping.

Wood impregnated by this method shows instance, several impregnated sticks of wood were tested by applying 100,000 volts between the ends thereof for about five minutes. The voltage. was then raised to 300,000 with no flash-over or injury to the wood. The sticks .were then immersed in Water for forty-eight.hours, being weighed before and after immersion, and showed less than one per cent absorption of-moisture. The sticks, after removal from the Water, were surface dried. after which a potential of 100,000-

volts was applied for five minutes. The

voltage was then gradually increased and it was found that the discharge flashed over at 'somewhat above 250,000 volts. Uponexamination, the Wood was found not to be injured in the least. The sticks were then subjected to varying voltages while a shower.

tion'whatsoever.

It is, obvious that materials other than ,paratfim-such as natural or artificial waxes,-

properties, may be used." The asphalt may- .greases, fats,-gums of low viscosity, 'etc.,-

which have great penetrating and insulating be replaced by tars, pitches, heavy gums,

cresols, and the like, which are insoluble in water andarenon-volatile and have 'insulating properties. It-is also apparent that various other changes may be made in practising my invention, all of which are considered to bewithin the scope thereof.

I claim as my invention:

1. A nfethod'of preparing an impregnated body ofwood which comprises drying the wood to a moisture content of 10 to 12%, impregnating the wood in a bath of parafiin at an elevated temperature and subsequently heating saidimpregnated wood in a bath of asphaltic material at a higher tempera] ture. 1

' 2. A method of impregnatingwood which consists in impregnating" the same with a wax at an'elevated temperature, and subsequently subjecting the same to impreg 'nation with a gummy material at a higher temperature.

3. A method of impregnating wood which consists in drying the same to reduce its moisture content to 10 to 12'per cent, then? impregnating the same with parafiin for live to SIX hours at a maximum tempcratureof 130 0., and subsequently subjecting the same to impregnation with asphalt for three or four hours at a temperature? of In testimony whereof, I have hereunto subscribed my name this 7th day of December 1920. v

OTHO V. STEWART. 

